Desulfurization of a heavy hydrocarbon fraction



3,551,328 DESULFURIZATION OF A HEAVY HYDROCARBON FRACTION Edward L. Coleand Raymond F. Wilson, Fishkill, and

Sheldon Herbstman, Spring Valley, N.Y., assignors to Texaco Inc., NewYork, N.Y., a corporation of Delaware No Drawing. Filed Nov. 26, 1968,Ser. No. 779,202 Int. Cl. (110g 29/22, 27/04 US. Cl. 208-240 15 ClaimsABSTRACT OF THE DISCLOSURE This invention relates to a process forreducing the sulfur content of heavy hydrocarbon petroleum fractions andmore particularly to the reduction in sulfur content of such hydrocarbonfraction by the oxidation of sulfur impurities and the subsequentremoval of such oxidized sulfur impurities by treatment with a lowerparaflinic hydrocarbon solvent.

Petroleum crude oils, and topped or reduced crude oils, as well as otherheavy hydrocarbon fractions and/or distillates including vacuum towerbottoms, atmospheric tower bottoms, black oils, heavy cycle stocks,visbreaker product effluent, etc., are contaminated by the presence ofexcessive concentrations of various non-metallic and metallic impuriteswhich detrimentally affect various processes to which such heavyhydrocarbon mixtures may be subjected. Among the non-metallic impuritiesis sulfur which exists in heteroatomic compounds and which effectivelypoisons various catalytic systems employed in a process for theconversion of such heavy hydrocarbon fractions to other hydrocarbonmaterials such as gasoline. Sulfur compounds are further objectionablebecause combustion of fuels containing these impurities results in therelease of sulfur oxides which are noxious, corrosive and in additionpresents a serious problem with respect to pollution of the atmosphere.

It is therefore an object of this invention to reduce the sulfur contentof heavy hydrocarbon fractions.

It has now been found that the sulfur content of heavy hydrocarbonfractions can be reduced by contacting a heavy hydrocarbon fractionwhich contains sulfur compounds with an oxidizing amount of an oxidantoptionally in the presence of an oxidation promoting catalyst, treatingsuch heavy hydrocarbon fraction which contains oxidized sulfur compoundswith a lower paraffinic hydrocarbon solvent in a concentrationsufiicient to separate at least a part of the oxidized sulfur compoundsfrom the heavy hydrocarbon fraction, separating the solvent-heavyhydrocarbon fraction from such oxidized sulfur compounds and recoveringa heavy hydrocarbon fraction of reduced sulfur content. Thus it has beendiscovered that the oxidation of sulfur impurities in a heavyhydrocarbon fraction in combination with a solvent treatment step usinga lower parafiinic hydrocarbon solvent produces a significant reductionin the sulfur content of the heavy hydrocarbon fraction, especially whencompared to the treatment of such sulfur-containing heavy hydrocarbonUnited States Patent Patented Dec. 29, 1970 fraction utilizing a singletreating step with a lower parafiinic hydrocarbon solvent.

In general the process of this invention is carried out by firstcontacting the heavy hydrocarbon fraction which contains sulfurimpurities (hereinafter referred to as sulfur containing hydrocarbonfraction) with an oxidizing amount of an oxidant for a time sufficientto effect oxidation of at least a part of the sulfur impurities presentin the sulfur containing heavy hydrocarbon fraction. The sulfurcontaining heavy hydrocarbon fraction which contains oxidized sulfurcompounds is then treated with a lower paraffinic hydrocarbon solvent ata concentration sufiicient to precipitate or obtain phase separation ofat least a part of the oxidized sulfur compounds from the heavyhydrocarbon fraction. The heavy hydrocarbon fraction of reduced sulfurcontent is then recovered from the oxidized sulfur compounds byconventional means, such as the separating of the solvent-heavyhydrocarbon fraction from the oxidized sulfur compounds and the removalof the parafiinic hydrocarbon solvent by distillation or vacuumstripping optionally using an inert stripping gas. As stated above, theoxidation step requires the oxidation of at least a part of the sulfurimpurities and the solvent treating step requires the precipitation orphase separation of at least a part of the oxidized sulfur compoundsfrom the heavy hydrocarbon fractions. By the use of the term at least apart is meant that the combined use of oxidation and solvent treatingsteps produces sulfur reduction in the heavy hydrocarbon fractiongreater than that obtained by the use of the solvent treating stepsingly in the absence of the oxidation step. Thus, the reduction insulfur content utilizing the process of this invention in general bringabout reductions in sulfur content 20% greater than the sulfur reductionobtained utilizing a single solvent treating step in the absence of theoxidation step.

The type of oxidant, the concentration of oxidant, the presence orabsence of an oxidation promoting catalyst (hereinafter referred to ascatalyst), the temperature and pressure during the oxidation step can bevaried over a wide range depending upon the nature of and the percentsulfur in such hydrocarbon fraction, the particular conditions beingthose conditions which effect oxidation of at least a part of the sulfurimpurities. In addition the conditions for solvent treating can bevaried over a wide range, both as to the ratio of volume of solvent tovolume of sulfur containing heavy hydrocarbon fractions, as well as totime, temperature, pressure, and the nature of and the percent sulfurpresent in the heavy hydrocarbon fraction. These conditions are adjustedin order to produce a solvent treating step wherein the solvent ispresent in a concentration sufficient to effect precipitation orseparation of at least a part of the oxidized sulfur compounds from theheavy hydrocarbon fraction and are adjusted in order to maximize thepercentage of oxidized sulfur compounds which are removed from the heavyhydrocarbon fraction.

In carrying out the oxidation step in the process of this invention anoxidant is utilized such as oxygen ineluding activated oxygen and air,ozone, organic peroxides, organic hydroperoxides, organic peracids,optionally in the presence of a metal containing catalyst.

Thus the oxidation step is carried out by contacting the sulfurcontaining heavy hydrocarbon fraction with an oxidant optionally in thepresence of a metal containing catalyst for a time sufficient to effectoxidation of at least a part of the sulfur present in the hydrocarbonfraction. The concentration of oxidant is usually dependent upon thepercent sulfur present in the heavy hydrocarbon fraction and in generalthe mole ratio of oxidant to sulfur is from about 0.5 to about 10 moleof oxidant per mole of sulfur, more preferably from about 1 to about 8moles of oxidant per mole of sulfur and still more preferably J fromabout 2 to about 5 moles of oxidant per mole of sulfur. When a catalystis employed, it is preferred that the catalyst concentration vary fromabout 0.0001 to about Wt. percent based upon the weight of the heavyhydrocarbon fraction, more preferably from about 0.10 to about 10 wt.percent, the catalyst concentration being sufficient to promote theeffectiveness of the oxidant. The temperature utilized in carrying outthe oxidation step can vary over a wide range and in general atemperature of from about 20 F. to about 450 F. is utilized, dependingupon the oxidant, although higher and lower temperatures can beutilized. In general the oxidant contacts the sulfur containing heavyhydrocarbon fractions for a time generally Within the range of fromabout minutes to 24 hours preferably from about one half hour to hours.The time that is utilized of necessity depends upon the percent sulfurpresent in the heavy hydrocarbon fraction and the type of oxidant. Thus,in the case of a gas, the time can vary over a wide range depending uponthe particular amount of gas such as ozone which is passed into thereaction mixture, that is, the rate of introduction of ozone into theheavy hydrocarbon fraction. In general for the oxidation step utilizingozone, a low temperature is utilized (such as from 20 F. to about 120F.) and the mole ratio of oxidant to sulfur within the above range canbe obtained during the time utilized during the oxidation step. Theprocess of this invention in general is carried out at atmosphericpressure although pressures above atmospheric for example up to about100 atmospheres can be utilized.

The preferred oxidants which are utilized in carrying out the oxidationstep of the process of this invention are ozone, organic peroxides,organic hydroperoxides and organic peracids. These oxidants areparticularly preferred since such oxidants have been found to giveexcellent reduction in percent sulfur when combined with the solventtreating step. In addition the use of the preferred oxidants have beenfound to be selective for oxidation of the sulfur compounds, that is,substantial amount of oxidation products such as acids and ketones arenot formed. In addition, high product yields in the oxidation step, bothas to the high product yield of oxidized sulfur impurities and the highproduct yield of heavy hydrocarbon fractions which remains after theoxidation step and in particular after the solvent treating step areobtained utilizing the preferred oxidants. The organic oxidants includeby way of example hydrocarbon peroxides, hydroperoxides and hydrocarbonperacids wherein the hydrocarbon radicals in general contains from about1 to about carbon atoms per linkage. With respect to the hydrocarbonperoxides and hydrocarbon hydroperoxides, it is particularly preferredthat such hydrocarbon radical contain from 4 to 18 carbon atoms perperoxide linkage and more particularly from 4 to 16 carbon atoms perperoxide linkage. With respect to the hydrocarbon peracids thehydrocarbon radical is defined as that radical which is attached to thecarbonyl carbon and in general such hydrocarbon radical can be from 1 toabout 12 carbon atoms more preferably from about 1 to about 8 carbonatoms. It is intended that the term organic peracid includes by way ofdefinition performic acid.

In addition it is contemplated within the scope of this invention thatthe organic oxidants can be prepared in situ, that is the peroxide,hydroperoxide or peracid can be generated in the sulfur containing heavyhydrocarbon fraction and such organic oxidant is contemplated for usewithin the scope of this invention.

Typical examples of hydrocarbon radicals are alkyl such as methyl,ethyl, butyl, t-butyl, pentyl, n-octyl and those aliphatic radicalswhich represent the hydrocarbon portion of a middle distillate orkerosene, cyclealkyl radicals such as cyclopentyl, alkylated cycloalkylradicals such as monoand polymethylcyclo-pentyl radicals, aryl andcycloalkyl substituted alkyl radicals such as phenyl and alkyl phenylsubstituted alkyl radicals examples of which are benzyl, methylbenzyl,caprylbenzyl, phenylethyl, phenylpropyl, naphthylmethyl, naphthylethyl,aryl radicals such as phenyl, and naphthyl, alkaryl radicals such asxylyl, alkylphenyl, and ethylphenyl.

Typical examples of oxidants are hydroxyheptyl peroxide, cyclohexanoneperoxide, t-butyl peracetate, di-tbutyl diperphthalate,t-butyl-perbenzoate, methyl ethyl ketone peroxide, dicumyl peroxide,t-butyl hydroperoxide, di-t-butyl peroxide, p-methane hydroperoxide,pinane hydroperoxide, 2,S-dimethylhexane-2,5-dihydroperoxide and cumenehydroperoxide, organic peracids, such as performic acid, peracetic acid,trichloroperacetic acid, perbenzoic acid and perphthalic acid.

The catalyst which is utilized to promote the oxidation of sulfur usingthe preferred oxidants are catalysts selected from Group IV-B, Group VBand Group VI-B metals. These catalysts can be incorporated into theoxidation system by any means known to those skilled in the art, and canbe either a homogeneous or heterogeneous catalyst system. The catalystcan be incorporated by a variety of means and by the use of a variety ofcarriers. The particular catalyst carrier which is utilized is notcritical with respect to the practice of this invention and can be forexample, a support medium or an anion (including complex formation)which is attached to the metal (e.g. a ligand). The particularlypreferred catalyst metals are titanium, zirconium, vanadium, tantalum,chromium, molybdenum and tungsten. Illustrative ligands include halides,organic acids, alcoholates, mercaptides sulfonates and phenolates. Thesemetals may be also bound by a variety of complexing agents includingacetonylacetonates, amines, ammonia, carbon monoxide and olefins,amongst others. The metals may also be introduced in the form oforganometallics including ferrocene type structures. The various ligandsillustrated above which are utilized solely as carriers to incorporatethe metal into the process system, in general have an organic radicalattached to a functional group such as the oxygen atom of carbonyloxygroup of the acid, the oxygen of the alcohol, the sulfur of themercaptan, the

of the sulfonate, the oxygen of the phenolic compound and the nitrogenof the amines. The organic radical attached to the afore describedfunctional groups can be defined as a hydrocarbon radical and in generalcan contain from 1 to about 30 carbon atoms. Typical examples ofhydrocarbon radicals are set forth above.

The metals contained on the heterogeneous catalyst can includeindividual or combinations of metals. These metals can be suspended on asuitable material, for example, alumina, silica (or combinations ofboth) as Well as activated clays or carbon, amongst others. The modes ofcontacting whereby the catalytic effect may be achieved may includeslurry-bed reactions or continuous contacting over a stationary phase ina trickle-tube reactor. The particularly preferred catalyst for carryingout the oxidation step of the process of this invention is molybdenumsuch as in the form of molybdenum hexacarbonyl.

The solvent treating step is carried out at any suitable temperature andpressure, the temperature and pressure being adjusted so as to maintainthe parafiinic hydrocarbon solvent (hereinafter referred to as solvent)in the liquid phase during the solvent treating step. A solvent treatingtemperature in the range of from about 50 F. to about 325 F., and apressure in the range of from about atmospheric to about atmospheres areemployed depending upon the composition of the solvent employed and tosome extent the composition of the heavy hydrocarbon fraction undergoingsolvent treating. Generally, a ratio of solvent to heavy hydrocarbonfraction in the range of from about 1 to 1 to about 20 to 1 is employedin the solvent treating step. The solvent treating step may be operatedunder substantially isothermal conditions or under a temperaturegradient, such as in the use of a solvent extraction tower where the topextraction temperature is greater than bottom extraction towertemperature by not usually more than about 40 degrees Fahrenheit. Alsoin the case of the use of a solvent extraction tower the solventtreating step may be operated so that the sulfur containing heavyhydrocarbon fraction is introduced thereinto at a number of points alongthe height of such extraction tower and/or so that the aliphatic solventis introduced thereinto at a number of points.

The paraffinic hydrocarbon solvent generally comprises one or moreparaifinic hydrocarbons having from 3 to carbon atoms in the molecule,examples of which are propane, butane, isobutane, pentane, isopentane,hexane, isohexane, heohexane, heptane octane and mixtures thereof.Instead of pure hydrocarbons or mixtures thereof, technical mixtures,such as paraffinic hydrocarbon oil fractions, e.g., light low-aromaticnaphtha fractions with boiling ranges between 50 F. and 350 F., may beused. These mixtures may also contain minor quantities of otherhydrocarbons as long as the paraffinic mixture as such retains thecharacter of at least a C to C hydrocarbon. In addition it iscontemplated within the scope of this invention that the paraffinichydrocarbon can contain a minor amount of additive materials to improvethe separation of the oxidized sulfur compounds from the heavyhydrocarbon fraction and/or otherwise increase the quality of thereduced sulfur containing heavy hydrocarbon fractions. Additives whichcan be used are for example, carbonates of aliphatic, cycloaliphatic,aromatic and heterocyclic compounds examples of which are methyl andethyl carbonates.

A wide variety of heavy hydrocarbon fractions and/or distillates may betreated, or made suitable for further processing, through theutilization of the method encom- 3 passed by the present invention. Suchheavy hydrocarbon fractions include full boiling range crude oils,topped or reduced crude oils, atmospheric distillates, vacuum towerbottoms, visbreaker bottoms product, heavy cycle stocks from thermallyor catalytically-cracked charge stocks, etc. The present method isparticularly well adaptable to the treating of crude oils and topped orreduced crude oils containing large quantities of asphaltenic material,and is especially advantageous when applied to the treating ofatmospheric or vacuum tower bottoms e.g. especially 550 F. or higherreduced crude oils at atmospheric pressure.

A particularly preferred heavy hydrocarbon fraction which can beutilized in the process of this invention are the deasphaltedatmospheric and 'vacuum residues which have been topped at temperaturesof a least 550 F. at atmospheric pressure. These deasphalted materialsin general are deasphalted according to conventional means such as theprocesses disclosed in US. Pat. No. 2,943,050 and U8. Pat. No.3,364,138.

The present invention can be carried out in batch, continuous orsemi-continuous operating cycles, and in one or more actual ortheoretical stages, employing contacting and separation equipment suchas has heretofore been employed in the selective solvent refining ofpetroleum stocks. In addition a multi-stage mode of operation that is arepeating of the process several times can be utilized in carrying outthe process of this invention. It should be understood that the specificequipment employed forms no part of the present invention.

The process of this invention can be better appreciated by the followingnon-limiting examples.

EXAMPLE 1 To a reactor equipped with stirrer and heating means ischarged 42160 grams of reduced Arabian Crude (550+F. 2.6 wt. percentsulfur, 6.03 wt. percent carbon residue) and 8854 grams of tertiarybutyl hydroperoxide (90% To this reaction mixture is added 126 grams ofa molybdenum catalyst 8% by weight molybdenum and 6 the mixture isheated to F. for a period of 60 hours. The reaction mixture is cooledand stabilized to remove tertiary butyl hydroperoxide decompositionproducts. This reaction mixture (250 grams) is then mixed with 2500milliliters of n-pentane in a glass separator at ambient temperature fora period of about 12 hours. Two layers are formed and the top layercontaining the heavy hydrocarbon fractions of reduced sulfur content isremoved and stripped of n-pentane solvent. The percent sulfur of theheavy hydrocarbon fraction is found to be 1.6 percent by weight with acarbon residue of 3.06 percent by weight.

EXAMPLE 2 The solvent treating step only of Example 1 is repeated using250 grams of the same reduced Arabian Crude (550+F.) and 2500milliliters of n-pentane. After the formation of two phases, theseparation of the solvent heavy hydrocarbon fraction layer and thestripping of solvent, the heavy hydrocarbon fraction has a percentsulfur of 2.6 weight percent and a carbon residue of 3.9 weight percent.

EXAMPLE 3 To a reactor equipped with stirrer and heating means is added1,000 grams of reduced Arabian Crude (550+F. 2.6 percent by weightsulfur, 6.03 percent by weight carbon residue) and 148 grams of tertiarybutyl hydroperoxide. To this mixture is added 5 grams of a molybdenumcatalyst containing 8% by weight molybdenum. The mixture is heated at188 F. for a period of 8 hours. The temperature is allowed to reachambient temperature and 250 grams of this material is mixed with 2500milliliters of n-pentane in a glass separator. Two layers are formed andthe top layer containing solvent and heavy hydrocarbon fraction isremoved and stripped of solvent. The heavy hydrocarbon fraction (reducedArabian Crude) has a percent sulfur of 1.79 percent by weight and acarbon residue of 3.07 percent by weight.

EXAMPLE 4 A Lago medium vacuum residuum (2.6% by weight sulfur, 6% byweight carbon residue) is charged to a deasphalting tower together withisobutane at a top deasphalting tower temperature of 264 F. a middletower temperature of 260 F. and a bottom tower temperature of 258 F. Thepressure is maintained at about 700 p.s.i.g. and a volume percent ofisobutane to vacuum residuum is maintained at about 490%. A deasphaltedresiduum is recovered from the deasphalting tower and charged to areactor. To the deasphalted residuum plus isobutane is charged tertiarybutyl hydroperoxide at a concentration of about 8% by weight based uponthe deasphalted vacuum residuum. To this mixture is charged a molybdenumcatalyst at a concentration of 0.10 wt. percent based upon the charge ofdeasphalted vacuum residuum. The temperature is maintained at about 200F. for an average residence time of about 1 /2 to 2 hours. The reactionmixture is transferred to a settler where it is contacted with about 10volumes of isobutane in countercurrent flow until phase separationoccurs. The heavy hydrocarbon fraction and solvent is removed from thesettler and the solvent removed. The heavy hydrocarbon fraction has areduced sulfur content of about 1.7% and a carbon residue of about 3.8weight percent.

Examples 1 through 4 clearly demonstrate the significant reduction insulfur content that is obtained utilizing the combination of oxidationstep plus solvent treating step with a paraffinic hydrocarbon solvent.More particularly, examples 1 and 2 demonstrate that the percent sulfurreduction obtained utilizing the process of this invention isconsiderably in excess of that which is obtained when utilizing asolvent treating step singly. Thus, in Example 1 the percent sulfur was1.76 wt. percent compared to a sulfur content of the starting materialof 2.6 percent, whereas in Example 2 a percent sulfur was obtained aftertreatment with pentane of 2.6 wt. percent.

7 Example 4 demonstrates that the process of this invention can becombined with additional processes such as a deasphalting process toproduce a combined process whereby deasphalting and desulfurizationoccurs to produce a material which has particular utility as a chargingstock.

While this invention has been described with respect to various specificexamples and embodiments it is to be understood that the invention isnot limited thereto and that it can be variously practiced within thescope of the following claims.

We claim:

1. A process which comprises contacting a heavy hydrocarbon fractionwhich contains sulfur compounds with 0.5 to about 10 mole of an oxidantper mole of sulfur present wherein said oxidant is selected from thegroup consisting of ozone, organic peracids, organic hydroperoxides,organic peroxides and their mixtures, thereafter treating said heavyhydrocarbon fraction containing oxidized sulfur compounds with a lowerparaffinic hydrocarbon solvent containing from 3 to 10 carbon atoms at aconcentration suflicient to separate at least a part of the oxidizedsulfur compounds from the heavy hydrocarbon fraction, separating theheavy hydrocarbon fraction from the oxidized sulfur compounds andrecovering the heavy hydrocarbon fraction of reduced sulfur content.

2. A process of claim 1 wherein the process is carried out in thepresence of an oxidation promoting catalyst selected from the groupconsisting of a group 4-B metal, a group 5-B metal, a group 6-B metaland mixtures thereof.

3. A process of claim 2 wherein the oxidant is selected from the groupconsisting of a hydrocarbon peroxide, a hydrocarbon hydroperoxide, ahydrocarbon peracid, performic acid and mixtures thereof wherein eachhydrocarbon radical contains from 1 to about 30 carbon atoms.

4. A process of claim 3 wherein each hydrocarbon radical contains fromabout 1 to about 12 carbon atoms.

5. A process of claim 4 wherein the oxidant is selected from the groupconsisting of tertiary butyl hydroperoxide, 40

cumene hydroperoxide and mixtures thereof.

6. A process of claim 1 wherein the lower parafiinic hydrocarbon solventcontains from 3 to 6 carbon atoms.

7. A process of claim 1 wherein the lower paraffinic hydrocarbon solventcontains from 3 to 6 carbon atoms.

8. A process of claim 2 wherein the lower paraflinic hydrocarbon solventcontains from 3 to 6 carbon atoms.

9. A process of claim 4 wherein the lower paraffinic hydrocarbon solventcontains from 3 to 6 carbon atoms.

10. A process of claim 5 wherein the lower paraffinic hydrocarbonsolvent contains from 3 to 5 carbon atoms.

11. A process of claim 1 wherein the heavy hydrocarbon fraction whichcontains sulfur compounds is a reduced crude oil.

12. A process of claim 1 wherein the heavy hydrocarbon fraction whichcontains sulfur compounds is a deasphalted reduced crude oil.

13. A process of claim 6 wherein the heavy hydrocarbon fraction whichcontains sulfur compounds is a deasphalted reduced crude oil.

14. A process of claim 7 wherein the heavy hydrocarbon fraction whichcontains sulfur compounds is a deasphalted reduced crude oil.

15. A process of claim 10 wherein the heavy hydrocarbon fraction whichcontains sulfur compounds is a deasphalted reduced crude oil.

References Cited UNITED STATES PATENTS 2,143,882 1/1939 Keith et a].20829O 2,110,845 3/1938 Whiteleg et a]. 19613 2,593,761 4/1952 Johnstone196-29 2,670,319 2/1954 Ayers et al 196-29 1,840,269 1/1932 Borstrom208-196 2,749,284 6/ 1956 Noble 208240 DELBERT E. GANTZ, PrimaryExaminer J. M. NELSON, Assistant Examiner U.S. Cl. X.R. 208196

